How much of the rib contact area is the gap in? In other words, where and how large in cross section is the gap?

Filling it with epoxy is a good idea, but you need to rough up the inside of the gap before you fill it so the new epoxy will stick well.

You could also cut off about 1/2" of covering all the way around the wing (careful not to cut the wood) and glass the joint. Then recover. Some people do this anyway.

Most of the strength in the wing joint is in the joiner that goes into the spars.